Hydroxy-functional polyester diluents as additives in coating compositions

ABSTRACT

This invention relates to novel hydroxy-functional polyester diluents, and more particularly, to acrylic-modified hydroxy-functional polyester reactive diluents useful for blending with a variety of thermosetting or thermoplastic film-forming polymers. More specifically, the hydroxy-functional polyester reactive diluents are essentially low molecular weight polyesters derived from triols, and a combination of unsaturated monocarboxylic acids and saturated monocarboxylic acids. These hydroxy-functional polyester diluents may be copolymerized with one or more acrylic monomers, i.e. hydroxy-functional acrylic monomers, and blended with a variety of thermosetting or thermoplastic film-forming polymers. These blends of the film-forming polymers and the hydroxy-functional polyester diluents can be crosslinked with conventional crosslinking agents such as isocyanates and used in the formulation of low VOC paint compositions particularly useful as automotive topcoats.

This is a divisional of application Ser. No. 07/815,658, filed on Dec.31, 1991, (now U.S. Pat. No. 5,248,717), which was in turn, a divisionalof Ser. No. 07/286,431, filed on Dec. 19, 1988, (now U.S. Pat. No.5,104,955), which was in turn, a divisional of Ser. No. 07/043,051,filed on Apr. 27, 1987, (now U.S. Pat. No. 5,004,828).

BACKGROUND OF THE INVENTION

This invention is directed to a novel hydroxy-functional polyester andmore specifically to an acrylic-modified hydroxy-functional polyesteruseful as a diluent with a wide variety of thermoplastic orthermosetting paint vehicles. More specifically, this invention isdirected to hydroxy-functional polyester diluents and acrylic-modifiedhydroxy-functional polyester diluents useful with a wide variety ofthermoplastic or thermosetting polymeric film-forming polymers.

The thermoplastic and thermosetting film-forming vehicles or polymerssuch as the polyurethanes, alkyds, acrylics, and polyesters arewell-known as vehicles of coating compositions and have been applied ona variety of substrates. The formulation of these vehicles in coatingscan be varied to optimize the desired performance characteristics.However, in some instances optimizing one characteristic can adverselyeffect the other desirable characteristics required of a particularcoating. For example, in refinishing automobile or truck bodies avariety of thermoplastic and thermosetting film-forming polymers areused and include such polymeric vehicles as the acrylic lacquers andenamels, the nitrocellulose lacquers, the alkyd enamels, the polyesterenamels, the polyurethane enamels and the like. These vehicles must havesufficient flexibility for application to various substrates, i.e. metalparts, but may not be sufficient for the more flexible plastic materialsutilized in today's automobile and truck bodies.

The hydroxy-functional polyester diluents, including theacrylic-modified polyester diluents of this invention have excellentcompatibility with a wide variety of film-forming polymers and areparticularly adaptable for use as automotive topcoats. Upon curing,these coatings form a glossy durable finish, exhibit excellent adhesionto metal with superior pigment dispersibility and are resistance tosolvents. The preferred coating can be formulated to contain more thanabout 75%, e.g. up to about 90%, by weight of non-volatile solids.Because of the strict solvent emission regulations of recent years, lowsolvent emission coatings have become very desirable and a number of lowVOC paint compositions have been proposed to meet these requirements.However, many of the available coatings are deficient in this regardbecause of the difficulty in application, adhesion, lack of flexibility,poor durability, poor pigment dispersibility and low solvent resistance.Therefore, many of these coatings are deficient for use as automotivetopcoats, especially when the topcoat includes a metallic flake as thepigment. The low viscosity of these coatings are not sufficient toimmobilize the flakes which tend to redistribute and thereby give anonuniform distribution in the film. The coatings of this invention,however, combine the desired characteristics, e.g. good pigmentdispersibility, etc., with the low application viscosity and aretherefore particularly adaptable for automotive and truck body topcoatsincluding coatings which use metallic flakes as the pigment.

The prior art required the use of mixtures of polyisocyanates withpolyesters such as disclosed in U.S. Pat. No. 4,451,600 and U.S. Pat.No. 4,419,293. These additives, however, are not adequate for preparingcoatings comprising polymeric low volatile organic compound (VOC)compositions adapted for use as automotive topcoats. Moreover, thecoating compositions of this invention are capable of being cured atambient temperatures, i.e. low bake and can be used in combination witha variety of pigments, including metallic flakes. Thus, the coatingcompositions of this invention have more than about 75% by weight ofnonvolatile solids exclusive of the pigment and other nonreactivecomponents and comprise a low molecular weight polyester with pendenthydroxy-functional groups and polymerizable double bonds and have anumber average weight ranging up to about 500 and more likely in therange of 140 to 300.

SUMMARY OF THE INVENTION

This invention relates to hydroxy-functional polyester diluents and morespecifically to acrylic-modified hydroxy-functional polyester diluentscapable of being blended with a wide variety of conventional vehicles,e.g. acrylics, alkyds, acrylic-modified alkyds, polyesters and the like.The coating compositions of this invention comprise up to about 75 partsby weight, i.e. from 1 to 75 parts by weight, of the hydroxy-functionalreactive diluent or its acrylic-modified polymer and from about 25 to 99parts by weight of a conventional film-forming thermoplastic orthermosetting resin and from 0 to 30 parts by weight of a crosslinkingagent which results in less than a 3.0-3.5 VOC coating curable atambient or room temperatures, i.e. low bake temperatures. Thehydroxy-functional polyester diluent and the acrylic-modified copolymersthereof have a number average molecular weight of between 100 and 500and preferably between 140 and 300 and comprise at least one hydroxyfunctionality, e.g. 1 to 2 hydroxyl groups, and at least one reactivedouble bond within the molecule. The reactive polyester diluents arederived from at least one polyol, i.e. a triol, at least one lowmolecular weight unsaturated monocarboxylic acid and at least one lowmolecular weight saturated monocarboxylic acid. The hydroxy-functionalpolyester reactive diluents may, if desired, be further modified with atleast one acrylic monomer, e.g. a hydroxy-functional acrylic monomer, toform the copolymer. The copolymer is obtained from 0 to 50 parts byweight of the acrylic monomer and 50 to 100 parts by weight of thehydroxy-functional polyester or the acrylic-modified hydroxy-functionalpolyester diluent.

Accordingly, it is an object of this invention to provide a novelhydroxy-functional polyester diluent compatible with a variety of paintvehicles. It is another object of this invention to provide anacrylic-modified hydroxy-functional polyester diluent compatible with avariety of conventional polymeric film-forming paint vehicles. It isanother object of this invention to provide a hydroxy-functionalpolyester reactive diluent and the acrylic-modified hydroxy-functionalpolyester diluents which can be crosslinked with a conventionalcrosslinking agent. It is a further object of this invention to providehydroxy-functional polyester reactive diluents capable of being blendedwith a variety of film-forming paint vehicles to form coatings whichcure at ambient or room temperature characterized as having less than3.0 to 3.5 VOC. It is a further object of this invention to provideunique coating compositions particularly useful for automotive bodiescomprising hydroxy-functional polyester reactive diluents and theacrylic-modified hydroxy-functional polyester reactive diluents for usein combination with a variety of thermosetting or thermoplasticfilm-forming vehicles.

These and other objects of the invention will become apparent from thefollowing description.

DETAILED DESCRIPTION OF THE INVENTION

More specifically, this invention relates to hydroxy-functionalpolyester reactive diluents having a number average molecular weightless than about 500 and preferably from about 140 to 300 characterizedas having at least one hydroxy group, e.g. from 1 to 2 hydroxy groups,per molecule with an average of at least one polymerizable double bondper molecule. The hydroxy-functional polyesters are derived from atleast one polyol, i.e. a triol, and at least one low molecular weightunsaturated monocarboxylic acid and at least one low molecular weightsaturated monocarboxylic acid. The polyol, i.e. triol, is present in astoichiometric amount to provide an excess number of hydroxyl groupswith the unsaturated monocarboxylic acid being present in an amountsufficient to provide at least one ethylenically unsaturated group foreach molecule of polyol. More specifically, the hydroxy-functionalpolyester diluents of this invention are derived from the reaction ofabout 40 to 60 parts by weight of at least one triol, 10 to 30 parts byweight of a low molecular weight unsaturated monocarboxylic acid, 10 to30 parts by weight of a low molecular weight saturated monocarboxylicacid and 0 to 15 parts by weight of a benzoic acid, i.e. tertiary butylbenzoic acid. The hydroxy-functional polyester diluents can be furthermodified with an acrylic monomer by reacting, for example, 50 to 100parts by weight of the hydroxy-functional polyester diluent having anumber average molecular weight less than about 500 with about 0 to 50parts by weight, e.g. 10 to 30 parts, of at least one acrylic monomercapable of copolymerizing with the hydroxy-functional polyester reactivediluent.

These hydroxy-functional polyester diluents and the acrylic-modifiedhydroxy-functional polyester diluents may be blended with conventionalthermosetting or thermoplastic film-forming polymers. More specifically,coating compositions may be prepared with a hydroxy-functional polyesterdiluent having a number average molecular weight less than about 500derived from the reaction of from about 40 to 60 parts by weight of atleast one triol, 10 to 30 parts by weight of the unsaturatedmonocarboxylic acid, 10 to 30 parts by weight of the saturatedmonocarboxylic and 0 to 15 parts by weight of a benzoic acid. Thehydroxy-functional polyester diluents or the acrylic-modifiedhydroxy-functional polyester diluents can be blended with 25 to 99 partsby weight of a conventional film-forming paint vehicle such as acrylicpolymers, alkyd polymers, polyesters and the like. Specifically, coatingcompositions can be prepared by blending approximately 1 to 75 parts byweight of the hydroxy-functional polyester diluent or preferably 10 to50 parts by weight of the hydroxy-functional polyester diluent or in thealternative the acrylic-modified hydroxy-functional polyester diluentwith approximately 25 to 99 parts by weight and preferably 50 to 90parts by weight of a conventional thermosetting or thermoplasticfilm-forming vehicle. Blends of the hydroxy-functional polyester diluentor the acrylic-modified hydroxy-functional polyester diluent blendedwith either a thermosetting or thermoplastic film-forming polymer maycontain up to 40 parts by weight of pigment such as titanium dioxide andvarious other conventional additives generally incorporated into paints.

The hydroxy-functional polyester diluents of this invention are preparedby reacting the triol, such as trimethylolpropane, with the unsaturatedmonocarboxylic acid, e.g. crotonic acid, and the saturatedmonocarboxylic acid, e.g. propionic acid, in a solvent such as xylene.The reactants are heated to temperatures ranging up to about 450° F.until a product is obtained which is characterized as having a numberaverage molecular weight (Mn) ranging from about 100 to 500 and has atleast one hydroxy-functional group and at least one reactive double bondwithin the molecule. These hydroxy-functional polyester reactivediluents can be further modified by reacting one or more acrylicmonomers such as the hydroxy-substituted acrylic monomers with thepolyester diluent at temperatures ranging up to about 325° F. Theacrylic monomer may be used to modify the hydroxy-functional polyesterdiluents in amounts ranging up to about 50 parts by weight, e.g. 1 to 30parts, of the acrylic monomer based on the total amount of the reactivepolyester diluent.

The polyols, i.e. the triols, preferably have molecular weight of lessthan about 200 and include such low molecular weight compounds astrimethylolethane, trimethylolpropane, glycerol and the like.

The low molecular weight unsaturated monocarboxylic acids are used inamounts ranging from about 10 to 30 parts by weight and preferably inamounts ranging from about 15 to 25 parts by weight. More specifically,the unsaturated monocarboxylic acids, such as crotonic acid, may becharacterized by the formula: ##STR1## wherein R₁ is either hydrogen oran alkyl group of 1 to 3 carbon atoms and R₂ is an aliphatic group of 1to 4 carbon atoms or an aryl group. The preferred unsaturatedmonocarboxylic acids include crotonic acid, tiglic acid, cinnamic acid,and various mixtures of any of these acids in any proportion.

The low molecular weight saturated monocarboxylic acids used inpreparing the hydroxy-functional polyester are used in amounts rangingfrom about 10 to 30 and preferably in amounts ranging from about 15 to25 parts by weight. The saturated mono-carboxylic acids arecharacterized by the formula:

    R--COOH

wherein R is hydrogen or a branched alkyl or straight chain alkyl orcyclic alkyl of 1 to 6 carbon atoms per molecule including suchmonocarboxylic acid as formic acid, acetic acid, butyric acid, pivalicacid, propionic acid, valetic acid, caproic acid, and combinationsthereof in any proportion. It may be desirable to use a small proportionof a benzoic acid by replacing some of either the unsaturated orsaturated monocarboxylic acids. Therefore, up to from about 15 parts byweight and preferably from 8 to 12 parts by weight of a benzoic acid maybe used together with the unsaturated monocarboxylic acid and thesaturated carboxylic acid in preparing the hydroxy-functional reactivepolyester diluents.

The hydroxy-functional polyester diluents prepared in accordance withthis invention may be further modified by copolymerization with at leastone acrylic monomer and preferably a hydroxy-substituted acrylicmonomer. The acrylic monomers are used in amounts ranging from about 0to 50 and preferably in amounts ranging from 1.0 to 30 parts by weightof at least one acrylic monomer, i.e. a hydroxy-substituted acrylicmonomer, with 50 to 100 parts by weight and preferably from about 70 to90 parts by weight of the hydroxy-functional polyester diluent. Thehydroxy-functional polyester diluents of this invention may be modifiedby copolymerizing the polyester with at least one acrylic monomerselected from the group consisting of the alkyl methacrylates, alkylacrylates, acrylic and methacrylic acids, and hydroxyl-containingacrylates, such as hydroxylalkyl acrylate or hydroxyalkyl methacrylateand any combination or mixtures of these vinyl monomers in anyproportion. More specifically, the preferred hydroxyalkyl acrylatesuseful for purposes of this invention, include not only the mono- andpolyacrylates such as the mono- or polyhydroxy alkyl di- andtriacrlyates or alkylacrylates, e.g. the methacrylates and ethacrylates,but also the halogen-substituted acrylates such as the chlorine orbormine-substituted mono- or polyhydroxy alkyl acrylates, e.g. the mono-or polyhydroxy alkyl chloroacrylates or hydroxychloroalkyl diacrylatesor dialkacrylates. More specifically, the hydroxyalkyl acrylates, forpurposes of this invention, may be characterized by the formula:##STR2## wherein R₂ is either hydrogen, a halogen, e.g. chlorine orbromine, an alkyl or substituted alkyl group, e.g. halogen-substitutedalkyl group wherein the alkyl group has 1 to 2 carbon atoms and R₃ is amono-or polyhydroxyalkyl or substituted alkyl, e.g. halogen-substitutedhydroxyalkyl group having up to 12 and preferably 2 to 8 aliphaticcarbon atoms.

In general, the acrylates may be described as esters of acrylic orsubstituted-acrylic acid including, for example, 2-hydroxypropylacrylate, 3-hydroxybutyl acrylate, 4-hydroxypentyl acrylate,5-hydroxypentyl acrylate, 5-hydroxyhexyl acrylate, 2-hydroxybutylacrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl chloroacrylate,2-hydroxyethyl acrylate, 2-hydroxyethyl ethacrylate, hydroxybutylethacrylate, 3-hydroxypropyl methacrylate, 3-hydroxypropylchloroacrylate, 3-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate,3-hydroxybutyl ethacrylate, 3-hydroxypropyl ethacrylate, 3-hydroxybutylchloroacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl2-chloroacrylate, 4-hydroxybutyl acrylate, 3-hydroxyethyl2-chloroacrylate, 3-hydroxybutyl chloromethacrylate, 5-hydroxypentylacrylate, 2-hydroxypropyl chloromethacrylate, 5-hydroxypentylmethacrylate, 6-hydroxyhexyl acrylate, 2-hydroxybutylchloromethacrylate, 2-hydroxyethyl chloroethacrylate, 3-hydroxybutylmethacrylate, 2-hydroxyethyl chloromethacrylate, 2-hydroxypropylchloroethacrylate, 2-hydroxybutyl dichloroethacrylate, 2-hydroxybutylchloromethacrylate, 3-hydroxypeopylchloromethacrylate, 3-hydroxypropylchloroethacrylate, 3-hydroxyhexyl chloromethacrylate, 3-hydroxypentyl2-chloroacrylate, 3-hydroxybutyl bromomethacrylate, 2-hyeroxybutylchloromethacrylate, 4-hydroxybutyl 2-chloroethacrylate, 3-hydroxypentyl2-chloroethacrylate, 3-hydroxypropyl 2-bromoethacrylate, 4-hydroxybutyl2-bromoethacrylate, 5-hydropxyhexyl methacrylate, 6-hydroxypentylchloromethacrylate and various other vinyl or acrylic esters containingat least one free alcoholic hydroxyl group, e.g. a mono- or polyhydroxyalkyl ester of acrylic, methacrylic or ethacrylic acid.

Other acrylic esters that can be used as the acrylic monomer have atleast one free hydroxyl group including polyethylene glycolmethacrylate, diethylene glycol methacrylate, triethylene methacrylate,tetraethylene glycol methacrylate, diproglycol pylene glycolmethacrylate, tetraethylene glycol chloroacrylate, tetraethylene glycolacrylate, tetraethylene glycol dichloroacrylate, glycerol methacrylate,pentaerythritol methacrylate, diethylene glycol monoacrylate,triethylene glycol monoacrylate, dipropylene glycol monoacrylate,trimethylol ethane diacrylate, trimethylol propane diacrylate,pentaerythritol triacrylate, glycerol acrylate, pentaerythritolmonoacrylate, trimethylol ethane monoacrylate, trimethylol propanemonoacrylate, trimethylol ethane chloroacrylate, trimethylol propanemethacrylate, trimethylol butane methacrylate, tetramethylene glycolchloroacrylate, triethylene glycol methacrylate, tetraethylene glycolacrylate, pentaerythritol dichloroacrylate, dipentaerythritoldiacrylate, dipentaerythritol triacrylate pentaerythritoldimethacrylate, pentaerythritol methacrylate and combinations of any ofthese hydroxy-containing acrylates in various proportions.

Styrenes that may be used in combination with the acrylic monomers maybe characterized by the formula: ##STR3## wherein R is hydrogen or analkyl group of 1 to 4 carbon atoms, e.g. tertiarybutyl styrene and maybe present in amounts ranging from about 0% to 70% and preferably inamounts ranging from 5 to 30 parts by weight of the total mixture ofacrylic monomers. The alkyl-substituted styrene may be either an ortho-,meta- or para- alkyl-substituted styrene such as para-substitutedtertiary-butyl styrene.

The hydroxy-functional polyester reactive diluents or theacrylic-modified hydroxy-functional polyester reactive diluents may beblended with conventional thermosetting or thermoplastic resins normallyused in the formulation of coatings. The polyester diluent including theacrylic-modified hydroxy-functional diluents may be blended in amountsranging from about 1.0 to 75 parts by weight of the polyester diluentwith 25 to 99 parts by weight and preferably 50 to 90 parts by weight ofthe thermosetting or thermoplastic film-forming polymers. Thesefilm-forming polymers are well known and include various paint vehiclessuch as the acrylic lacquers and enamels, nitrocellulose lacquers, alkydenamels, polyester enamels and polyurethane enamels.

The acrylic film-forming polymers are typically polymers or copolymersof one or more alkyl esters of acrylic acid or methacrylic acid,optionally together with one or more other ethylenically unsaturatedmonomers. Suitable acrylic esters for either type of polymer includemethyl methacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, ethyl acrylate, butyl acrylate, vinyl acetate,acrylonitrile, etc. Where the polymers are required to be of thecrosslinking type, suitable functional monomers which can be used inaddition to those already mentioned include acrylic or methacrylic acid,hydroxy ethyl acrylate, 2-hydroxy propyl methacrylate, glycidylacrylate, tertiary-butyl amino ethyl methacrylate, etc. If desired, theacrylic polymers can be modified by the incorporation of alkyd polymersas well.

Typically, the acrylics are prepared by conventional free radicaladdition polymerization techniques. If desired, the polymerization canbe catalyzed by conventional catalysts known in the art such as azo,peroxy, or redox catalysts. Typically, the acrylic monomers are heatedat temperatures ranging from about 180° F. to 400° F. and especially200° F. to 300° F. to effect the polymerization. It is normallypreferred to prepare the polymers by solution polymerization in inertorganic solvents.

Representative acrylic lacquers are described in U.S. Pat. No. 4,168,249and representative acrylic alkyd enamels are described in U.S. Pat. No.3,844,993. Representative acrylic enamels are taught in U.S. Pat. No.4,124,551. The teachings of all these patents are hereby incorporated byreference. Commercially available acrylic lacquers include those soldunder various trade designations such as "Pro-Kril" by Acme, a marketingunit of Sherwin-Williams, "Lucite" by the DuPont Co., and "Duracryl" byDitzler.

Nitrocellulose lacquers are also well known and commercially availablenitrocellulose lacquers include those sold under the trade designation"Duco" by DuPont Co.

Thermosetting alkyd or polyester enamels are also well known and can beprepared in a known manner by the condensation of polyhydric alcoholsand polycarboxylic acids or anhydrides, with or without the inclusion ofnatural drying oil fatty acids. The polyesters or alkyds may contain aproportion of free hydroxyl and/or carboxyl groups which are availablefor reaction, if desired, with suitable crosslinking agents.

Polyurethane vehicles are also well known and can be prepared in a knownmanner by the reaction of polyhydric alcohols and polyisocyanates.Representative acrylic polyurethane enamels are described in U.S. Pat.No. 3,558,564 and the teaching of which is hereby incorporated byreference.

When these film-forming vehicles are thermosetting vehicles, they willtypically also contain a crosslinking agent such as a polyisocyanate,which may be blocked, a polyepoxide, or a nitrogen resin such as acondensate of an aldehyde, typically formaldehyde, with a nitrogenouscompound such as urea, melamine or benzoguannamine or a lower alkylether of such a condensate. In those cases where the coating compositioninvolves a thermosetting vehicle having functional groups which arereactive with an isocyanate it is usually necessary to add theisocyanate shortly before the application of the coating to minimize theincrease of viscosity resulting from the reaction of the isocyanategroups with the reactive groups on the thermosetting vehicle.

The following illustrates the hydroxy-functional and acrylic-modifiedhydroxy-functional polyester diluents and the method of preparing saidpolyester diluents in accordance with this invention.

EXAMPLE 1 Hydroxy-Functional Polyester Diluent

A 5-liter reactor equipped with a mechanical stirrer, reflux condenser,thermometer, nitrogen inlet, Dean-Stark water trap and heating mantlewas charged with 1,788 parts by weight of trimethylolpropane, 860 partsby weight of crotonic acid, 740 parts by weight of propionic acid and200 parts by weight of xylene. The reactants were heated to 450° F. andwere processed to an acid number of 2 to 3. A hydroxy-functionalpolyester having a number average molecular weight of 146, as determinedby gel permeation chromatography using polystyrene as the standard wasobtained.

EXAMPLE 2 Acrylic-Modified Hydroxy-Functional Polyester

A 5-liter polymerization reactor equipped with a mechanical stirrer,reflux condenser, thermometer, nitrogen inlet, Dean-Stark water trap,heating mantle and fluid metering pump was charged with 2,398 parts byweight of the hydroxy-functional polyester diluent of Example 1 andheated to 320° F. under nitrogen. A monomer mixture comprised of about118 parts by weight of styrene, 102 parts by weight of methylmethacrylate, 169 parts by weight of butyl methacrylate, 160 parts byweight of hydroxyethyl methacrylate, 10 parts by weight of methacrylicacid and 25 parts by weight of tertiary butyl perbenzoate was meteredinto the polymerization reactor at a uniform rate over a period of 3hours. Additional amounts of tertiary butyl perbenzoate (10 parts byweight) were added over about 30 minutes at 320° F. Heating of thereactants was maintained at reflux for an additional 2 hours. Anacrylic-modified hydroxy-functional polyester diluent was obtainedhaving a number average molecular weight of 270, as determined by gelpermeation chromatography using polystyrene as the standard.

EXAMPLE 3 Acrylic-Modified Hydroxy-Functional Polyester

A 5-liter polymerization reactor equipped with a mechanical stirrer,reflux condenser, thermometer, nitrogen inlet, Dean-Stark water trap,heating mantle and a fluid meter pump was charged with 701 parts byweight of the hydroxy-functional polyester diluent of Example 1 andheated to 320° F. under nitrogen. A monomer mixture comprising 59.5parts by weight of styrene, 56.3 parts by weight of methyl methacrylate,85.1 parts by weight of butyl methacrylate, 80.5 parts by weight ofhydroxyethyl methacrylate, and 17.6 parts by weight of tertiary butylperbenzoate were metered into the polymerization reactor at a uniformrate over a 3 hour period. Additional amounts of the tertiary butylperbenzoate (10 parts by weight) scavenger catalyst were added over 30minutes at 320° F. Heating was maintained at reflux for an additional 2hour period. An acrylic-modified hydroxy-functional polyester diluentwas obtained and characterized as having a number average molecularweight of about 200, as determined by gel permeation chromatographyusing polystyrene as the standard. These hydroxy-functional polyesterdiluents, including the acrylic-modified hydroxy-functional polyesterdiluent, (Examples 1, 2, and 3) were blended with film-forming polymers,i.e. hydroxy-functional acrylates containing isocyanates, in the ratioof 30 parts by weight of the hydroxy-functional polyester diluents with70 parts by weight of the hydroxy-functional acrylic containing theisocyanate as illustrated in the data of Tables 1, 2 and 3.

EXAMPLE 4

A 5-liter reactor equipped with a mechanical stirrer, reflux condenser,thermometer, nitrogen inlet, Dean-Stark water trap and heating mantlewas charged with 492.2 parts by weight trimethylol propane, 225.3 partsby weight crotonic acid, 193.8 parts by weight propionic acid, 88.7parts by weight para-t-butyl benzoic acid and 50 parts xylene as reflexsolvent. This is then heated to 450° F. and approximately 103 grams ofwater is removed. The vehicle is processed to an acid number 2 to 3. Ahydroxy-functional polyester, having a number average molecular weightof 160 as determined by gel permeation chromatography using polystyreneas standard, was obtained. Theoretical number average molecular weight,was 242 and hydroxyl number was 329.

The formulation of the hydroxy-functional polyester and acrylic-modifiedhydroxy-functional polyester diluents with conventional thermosettingand thermoplastic film-forming resins are illustrated in the followingTables:

                  TABLE I                                                         ______________________________________                                        RESIN COMPOSITION AND CHARACTERISTICS                                                      Percent By Weight                                                             Example 1                                                                             Example 2 Example 3                                      ______________________________________                                        Reactants                                                                     Trimethylolpropane                                                                           54.21     --        --                                         Crotonic Acid  26.07     --        --                                         Propionic Anhydride                                                                          19.72     --        --                                         Example 1      --        80.14     70.10                                      Styrene        --        3.94      5.95                                       Methyl Methacrylate                                                                          --        3.41      5.63                                       Butyl Acrylate --        5.65      8.51                                       Hydroxyethyl   --        5.34      8.05                                       Methacrylate                                                                  Methacrylic Acid                                                                             --        0.35      --                                         t-butyl perbenzoate                                                                          --        1.17      1.76                                       Solvent        Xylene    Xylene    Xylene                                     Characteristics                                                               % NVM (Theo.)  98.0      98.0      98.0                                       Viscosity      G         13-16     40+                                        AV             2.3       5.9       4.2                                        Color (G&H)    2         1-2       1-2                                        Clarity        CLR       CLR       CLR                                        OH. Eq. Wt.    171       200       211                                        (solid resin)                                                                 M.sub.w        177       1,600     1,000                                      M.sub.n        146       270       200                                        P.sub.d        1.2       5.9       4.6                                        Hydroxyl Number*                                                                             305       256       221                                        ______________________________________                                         *Measured.                                                               

                  TABLE II                                                        ______________________________________                                        VISCOSITY STUDY AND POT LIFE OF LOW                                           VOC COATINGS                                                                  (Blend of Polyester Diluents with                                             Film-Forming Acrylic and Isocyanate)                                          Polyester Diluents                                                                           Example 1 Example 2 Example 3                                  ______________________________________                                        Init. Visc.*   23"       26"       29"                                        1 Hr.          25"       29"       29"                                        2.5 Hrs.       29"       36"       35"                                        3.5 Hrs.       32"       38"       42"                                        4.5 Hrs.       35"       43"       45"                                        5.5 Hrs.       41"       49"       51"                                        VOC            3.43      3.43      3.43                                       % NVM          59.15     59.29     59.32                                      Eq. Wt.        117       138       151                                        NCO/OH Ratio   .70/1.0   .78/1.0   .84/1.0                                    Clear Blend with                                                              Hydroxy-Functional                                                            Acrylic Polymer (70/30)                                                       Init. Visc.    18"       16"       15"                                        VOC            3.13      3.12      3.10                                       % NVM          62.00     62.04     61.97                                      ______________________________________                                         *Viscosity increase with time  #2 Zahn cup (hydroxyfunctional acrylic         polymer with isocyanate)                                                 

                  TABLE III                                                       ______________________________________                                        FILM PROPERTIES WITH FILM-FORMING POLYMERS**                                  Polyester Diluents*                                                                          Example 1 Example 2 Example 3                                  ______________________________________                                        Air Dry                                                                       Tape Test                                                                     8 Hrs.         Tacky     Tacky     Tacky                                      24 Hrs.        Pass      Pass      Pass                                       Appearance     No Haze   No Haze   No Haze                                    Pendulum Hardness                                                                             9        24        33                                         (24 Hrs.)                                                                     Gloss 20°/60°                                                                  72.2/87.3 81.0/87.2 80.3/87.1                                  Solvent (MEK) 24 Hrs.                                                                        Pass      Pass      Pass                                       Force Dry - 180° F./                                                   30 min.                                                                       Tape Test - 8 Hrs.                                                                           Fail      Pass      Pass                                       Appearance     No Haze   No Haze   No Haze                                    Pendulum hardness                                                                             7        20        80                                         (24 Hrs.)                                                                     Gloss 20°/60°                                                                  82.4/87.7 81.1/88.5 83.9/89.4                                  Solvent (MEK) 24 Hrs.                                                                        Pass      Pass      Pass                                       ______________________________________                                         *30% blend of polyester diluent in 70% of acrylic filmforming polymers.       **Acrylic polymer containing isocyanate crosslinking agent.              

                                      TABLE IV                                    __________________________________________________________________________    POLYESTER DILUENT COMPOSITIONS AND CHARXCTERISTICS                            Components   Control*                                                                           Example 5                                                                           Example 6                                                                           Example 7                                       __________________________________________________________________________    Trimethyol Propane                                                                         52.77                                                                              49.23 59.24 52.77                                           Crotonic Acid                                                                              25.38                                                                              22.53 28.49 25.38                                           Propionic Acid                                                                             21.85                                                                              19.38 12.27 21.85                                           p-t-butyl Benzoic Acid                                                                          8.86  --    --                                              NVM (Theo.)  98%  98%   98%   98%                                             Viscosity    G-H  F-G   M-N   F-G                                             Aci Value    2.5  3.9   2.7   3.2                                             Color        2    2     2     2                                               Clarity      Clear                                                                              Clear Clear Clear                                           OH Eq. Wt.   152  144   110   171                                             (Solid Resin                                                                  Hydroxyl Number (Theo.)                                                                    368  329   507   368                                             M.sub.n (Theo.)                                                                            227  242   206   226                                             __________________________________________________________________________     *Control is Example 1 with 2% by weight of xylene.                       

                  TABLE V                                                         ______________________________________                                        PERFORMANCE PROPERTIES OF LOW                                                 VOC SYSTEMS (TOPCOAT)                                                                       Control                                                                              Example 5 Example 6                                      ______________________________________                                        Clear                                                                         (Uncatalyzed)                                                                 Initial Visc.   18"      14"       15"                                        #2 Zahn Cup                                                                   VOC             3.13     3.07      3.09                                       NVM             62%      62.1%     62.1%                                      Black                                                                         Acrylic Polymer with                                                          Isocyanate                                                                    Initial Viscosity                                                                             23"      27"       29"                                        1 Hr.           --       --        --                                         2 Hrs.          29"      35"       40"                                        (Air Dry)                                                                     Hand Slick (4.5 Hrs.)                                                                         Pass     Pass      Pass                                       Wt/Gal.         8.40     8.10      8.15                                       NCO/OH          --       1.2/1     1.2/1                                      Tape Test (16 Hrs.)                                                                           Pass     Pass      Pass                                       DFT             --       2.6       2.0                                        Appearance      No Haze  No Pop    Pop                                                                 Sl. Peel  Sl. Peel                                   Pend. Hardn. (40 Hrs.)                                                                        9-       40        62                                         Gloss                                                                         20°      72.2     83.5      85.4                                       60°      87.3     91.0      91.6                                       Solvent (MEK) 24 Hrs.                                                                         Pass     Pass      Pass                                       DIO             --       87.4      77.9                                       Across Grain DOI                                                                              --       90.8      83.8                                       (Force Dry) - 30 Min. @                                                        180° F.                                                               Tape Test       Fail     Pass      Pass                                       DFT             --       1.85      2.31                                       Appearance      No Haze  No Pop    Pop                                                                 Sl. Peel  Sl. Peel                                   Pend. Hard. (24 Hrs.)                                                                         7        24        47                                         Gloss                                                                         20°      82.4     82.7      81.1                                       60°      87.7     90.2      90.8                                       DOI             --       74.9      70.0                                       Across Grain DOI                                                                              --       87.4      84.0                                       Solvent (MEK)   Pass     Pass      Pass                                       ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        (paint formula)                                                                                      Parts By                                               Components             Weight                                                 ______________________________________                                        Polyester Diluent of Example 1 with                                                                  10 to 90                                               Acrylic Film-Forming Polymer (30/70)                                          Organic Solvent         0 to 30                                               Pigment (i.e. TiO.sub.2)                                                                             10 to 40                                               Fillers (e.g. Carbonates)                                                                             0 to 30                                               Extenders               0 to 30                                               Driers                 0.01 to 10                                             Catalyst (e.g. Cobalt Salts)                                                                         0.01 to 1.0                                            Defoamers (e.g. Silicones)                                                                           0.01 to 2.0                                            ______________________________________                                    

Typically, the coating composition will include other additives toadjust the performance and application characteristics of the coating.Normally, the coating composition will include an inert organic solventtypically ranging from 1.0 to 30% by weight based upon the total weightof the coating. Useful inert solvents for the coating compositioninclude aromatic hydrocarbons such as toluene, xylene, ethyl benzene,aromatic naphtha, etc.; aliphatic hydrocarbons such a mineral spirits,hexane, aliphatic naphtha, etc.; esters such a butyl acetate, ethyleneglycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate,etc.; and ketones such as ethyl amyl ketone, etc.

The coating may also contain other additives such as flow agents,catalysts, ultra violet light absorbers, etc. The coating may be appliedto any substrate, such as metal, plastic, wood, glass, synthetic fibers,etc. by brushing, dipping, roll coating, flow coating, spraying or othermethod conventionally employed in the coating industry. If desired, thesubstrate may be primed prior to the application of the coating.

Typical pigments used in the coating compositions include the variousmetal oxides, such as titanium dioxide, zinc oxide, iron oxide, andmetal flakes, such as aluminum or bronze flakes, metal powders, and themolybdate pigments, such as molybdate, orange pigments, sulfatepigments, carbonate pigments, carbon black, silica pigments and variousother organic or inorganic pigments commonly used in the preparation ofcoatings. Pigments are generally based on the weight of the binder orvehicle in a ratio of about 0.5-100 to 200-1 where the binder or vehicleis the film forming constituent of the coating. In formulating paints,it is a practice in addition to including the primary pigments, such asTiO₂, to use other materials such as fillers or extenders, e.g. thecarbonates, talcs, silicates, clays, micas, and the like in combinationwith the primary pigment. The relative proportion of the primary pigmentand the fillers or extenders is not critical and may be varied over awide range. Generally, however, the primary pigments are present at apigment volume concentration to provide the desired paint covering orhiding, whereas the extender pigment is present in amounts to providethe paint with the total required pigment volume concentration.

While this invention has been described with respect to a number ofspecific embodiments, it is obvious that there are other variations andmodifications which can be made without departing from the spirit andscope of the invention as more particularly set forth in the appendedclaims.

The invention claimed is:
 1. A coating composition comprising fromaboutI. 1.0 to 75 parts by weight of an acrylic modifiedhydroxy-functional polyester diluent obtained by the reaction of:A. 50to 100 parts by weight of a hydroxy-functional polyester having a numberaverage molecular weight less than 500 derived from the reaction of fromabout(a) 40 to 60 parts by weight of at least one triol having amolecular weight less than about 200, (b) 10 to 30 parts by weight of anunsaturated monocarboxylic acid having the formula: ##STR4## wherein R²is either hydrogen or an alkyl group of 1 to 3 carbon atoms and R₂ is analiphatic group of 1 to 4 carbon atoms or an aryl group, (c) 10 to 30parts by weight of a saturated monocarboxylic acid having the formula:

    R--COOH

wherein R is hydrogen or a branched alkyl or straight chain alkyl of 1to 6 carbon atoms, and (d) 1 to 15 parts by weight of a benzoic acid;with B. 1 to 50 parts by weight of at least one acrylic monomercopolymerizable with said hydroxy-functional polyester; II. 25 to 99parts by weight of a thermosetting or thermoplastic film-formingpolymer, and III. 0 to 40 parts by weight of an inorganic pigment. 2.The coating composition of claim 1 further characterized in that atleast one of the acrylic monomers copolymerizable with saidhydroxy-functional polyester is a hydroxy-functional acrylic monomer. 3.The coating composition of claim 1 further characterized in that theinorganic pigment comprises titanium dioxide.
 4. The coating compositionof claim 1 further characterized in that the film-forming polymer is athermoplastic polymer present in an amount ranging from about 50 to 90parts by weight.
 5. The coating composition of claim 1 furthercharacterized as incorporating an effective amount of a crosslinkingagent selected from the group consisting of amine aldehydes andisocyanates.
 6. The coating composition of claim 5 further characterizedin that the crosslinking agent is present in an amount ranging up toabout 30 parts by weight based on the combination of the diluent and thefilm-forming polymer.
 7. The coating composition of claim 4 furthercharacterized in that a crosslinking agent is present in an amountranging up to about 30 parts by weight based on the combination of thediluent and the film-forming polymer.
 8. The coating composition ofclaim 7 further characterized in that the crosslinking agent is selectedfrom the group consisting of amine aldehydes and isocyanates.
 9. Thecoating composition of claim 2 further characterized in that aneffective amount of a crosslinking agent is present in an amountsufficient to crosslink the hydroxy-functional diluent and thefilm-forming polymer.